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Gas turbine engine curved diffuser with partial impingement cooling apparatus for transitionsRelated Patent Categories: Power Plants, Combustion Products Used As Motive Fluid, Combustion Products Generator, Having Diffuser For Air InletGas turbine engine curved diffuser with partial impingement cooling apparatus for transitions description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20070175220, Gas turbine engine curved diffuser with partial impingement cooling apparatus for transitions. Brief Patent Description - Full Patent Description - Patent Application Claims
FIELD OF THE INVENTION [0001] The invention generally relates to a gas turbine engine with a compressor for supplying air. More particularly, it relates to an assemblage of components providing compressed air in a can-annular combustion chamber arrangement, where a portion of the air is directed for cooling transitions. BACKGROUND OF THE INVENTION [0002] In gas turbine engines air usually is compressed at an initial stage, then is heated in combustion chambers, and the hot gas so produced drives a turbine that does work, including rotating the compressor. [0003] To achieve a good overall efficiency in a gas turbine engine, one consideration is the reduction of losses of air pressure, such as due to friction and turbulence, between the air compressor and the intakes of the combustion chambers. In a common gas turbine engine design, compressed air flows from the air compressor, through a diffuser, into a plenum in which are positioned transitions and other components, and then from the plenum into the intakes of combustion chambers. [0004] One general approach to improve airflow efficiency in the plenum, and thereby improve overall efficiency, is to modify the end of the diffuser so as to redirect air more radially outward. For example, a curved diffuser may be employed wherein the outlet end has a bend that directs the airflow radially outward, instead of axially aft. Conceptually this may provide 1) a more direct, flow-efficient route to the combustion chamber intakes, and 2) less travel and turbulence/losses in the parts of the plenum where the mid-sections and aft ends of the transitions are located. [0005] However, radial diversion of a substantial portion of compressed air, without more, may present a problem when the airflow from the compressor has been used, or is desired to be used, to cool the transitions. Generally, transition cooling may be effectuated fully or partially by any of the following, which represents a non-exclusive list: closed circuit steam cooling (i.e., see for one example U.S. Pat. No. 5,906,093); open air cooling (in which a portion of the compressed air passes through channels in the transition and then enters the flow of combusted gases within the transition, see for one example U.S. Pat. No. 3,652,181); convection cooling (see for one example U.S. Pat. No. 4,903,477); effusion cooling (i.e., conveying air from outside the transition through angled holes into the transition); channel cooling (i.e., conveying air from outside the transition, through channels in the transition walls, and into the transition); and impingement cooling (where air is directed at the transition exterior walls through apertures positioned on plates or other structures close to these walls, see U.S. Pat. No. 4,719,748 for one example). It also is noted that some of these approaches may be used in combination with one another. [0006] Notwithstanding the features of current cooling approaches, when compressor air is desired to cool the transition, and when a more efficient design, such as a curved diffuser, is desired for airflow, there is a need for an appropriately designed combination of airflow-directing elements to attain a reliable, desired balancing of overall airflow efficiency and of transition cooling. As disclosed in the following sections, the present invention provides airflow-directing assemblages that are effective to achieve this desired balance. That is, the present invention advances the art by solving the dual, potentially conflicting issues of cooling of transitions and conservation of airflow and pressure to the combustion chambers. BRIEF DESCRIPTION OF THE DRAWINGS [0007] The foregoing and other features of the invention will be apparent from the following more particular description of the invention, as illustrated in the accompanying drawings: [0008] FIG. 1 is a schematic depiction of a gas turbine engine such as may comprise various embodiments of the present invention. [0009] FIG. 2A is a cross-sectional view of a portion of the gas turbine engine depicted in FIG. 1, further depicting an embodiment of the present invention. FIG. 2B provides a schematic upstream-directed view from the line A-A of FIG. 2A, with the transitions sectioned at line B-B of FIG. 2A, with a partial cut-away. FIG. 2C provides a top outboard view of a portion of the plate depicted in FIGS. 2A and 2B that shows an array of apertures on the outboard surface. [0010] FIG. 3A provides a side cross-section view of a section of a gas turbine engine taken through a port of a curved diffuser, depicting a conduit-type embodiment of the present invention. FIG. 3B provides a top outboard view of the conduit depicted in FIG. 3A. FIG. 3C provides a schematic upstream-directed view from the line A-A of FIG. 3A, with the transitions sectioned at line B-B of FIG. 3A. [0011] FIGS. 4A and 4B depict alternative arrangements of conduits and respective transitions using the same type of side cross-section view as used in FIG. 3C. DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS [0012] The present invention addresses the problems related to balancing the cooling of transitions of a gas turbine engine and efficient airflow through a plenum in which are positioned those transitions. These problems are solved with an assemblage of components adapted to provide a primary portion of air from the compressor efficiently directed to the intakes of the combustion chambers and a lesser, secondary portion of air directed to cool the transitions. One component comprises a diffuser comprising a arcuate surface, for example a curved outlet end, that directs the primary portion (taken to mean over 50 percent of the total flow) of the compressed air radially outwardly, and that also comprises a plurality of spaced-apart ports. These ports are adapted to provide the secondary portion of the compressed air to a second component, for cooling of the transitions. [0013] The second component comprises a pressure boundary element, which comprises an array of apertures disposed a distance from respective transitions to provide impingement cooling. The pressure boundary element has an upstream end disposed about the arcuate surface so as to define a confined space through which air of the secondary portion passes, from the ports through the apertures, to effectuate, during operation of the gas turbine engine, the aforementioned impingement cooling. Examples of the pressure boundary element include a flat plate or a curved plate (or a number of these arranged circumferentially) that comprise arrays of apertures, and a conduit (or a number of these arranged circumferentially) disposed between respective ports and transitions. [0014] By the term "curved diffuser" is meant a diffuser comprising an arcuate surface at its outlet end effective to direct the airflow passing through the bend radially outward by at least 30 degrees relative to the longitudinal axis of the gas turbine engine, and preferably at least 45 degrees. The arcuate surface provides for a more direct routing of the primary portion of compressed air to the combustion chamber intakes. [0015] However, as noted without more such curved diffuser would not provide for effective cooling of the transitions, particularly to those more aft transition areas that are not affected by this primary portion airflow. The discovery of the present invention was in part related to the realization that impingement cooling need not be effectuated by the orthodox approach of affixing impingement plate around a transition. This realization was combined with the strategies regarding improving performance by redirecting air with a curved diffuser, however, realizing that by providing ports through such diffuser a relatively smaller portion of air could be supplied to non-affixed impingement cooling structures to cool, at a minimum, lower (inboard) surfaces of the transition. This results in transitions that are not surrounded by affixed impingement cooling structures (these being affixed to the curved diffuser and other structures), which results in easier access for repairs and maintenance. [0016] Thus, the provision of ports through the arcuate surface of the curved diffuser provides air to cool those more aft transition areas that are not affected by the primary portion airflow. This air flows through apertures in a pressure boundary element to provide impingement cooling. As noted above, this approach to cooling differs structurally from impingement cooling in which the impingement plates surround and are structurally connected to respective transitions. In some embodiments, the pressure boundary element comprises one or a plurality of plates arranged inboard of mid and aft sections of the transitions so as to be in sufficient proximity for impingement cooling. This pressure boundary element is supplied by the plurality of spaced-apart ports, which are positioned in the arcuate surface of the curved diffuser. Air flowing from these ports supplies this impingement cooling apparatus selectively by passing into a confined space defined in part by the arcuate wall and one or more of the plates in proximity to and inboard of the transitions. In other embodiments, conduits are in fluid communication with the ports and comprise arrays of apertures that provide for impingement cooling of the transitions. Such conduits are positioned so that the airflow from the apertures is effective to provide the impingement cooling to transitions. [0017] The examples below thus demonstrate a functionally split air flow that is effective to direct air in the plenum in a collaborative manner so to provide adequate cooling without the losses (volume or pressure) associated with known arrangements of elements for directing air and cooling the transitions. [0018] Differences between the present solution to the above-indicated problems and previous approaches may be summarized as follows. One previous approach may be exemplified by the teachings of U.S. Pat. No. 4,719,748, issued Jan. 19, 1988 to Davis et al. (the '748 patent). In the '748 patent, an axial diffuser would provide air substantially axially and downstream into a plenum in which are disposed transitions. An impingement sleeve surrounds each transition forming a channel. Apertures arranged in the impingement sleeve provide for air to pass into the channel to cool the respective transition. One feature is that the channel becomes wider at the upstream discharge end compared to the downstream, turbine end. The areas of the apertures closer to the upstream discharge end are larger than the areas of apertures (for a given surface area) closer to the downstream turbine end. This configuration is stated to provide an increased mass flow rate without requiring an increase in pressure drop. However, there is no provision for efficient passage and redirection of the substantial portion of air flowing from the compressor, and the form of impingement cooling is a shell closely conforming to the shape of, and thereby surrounding, the transition. The '748 patent also discloses film cooling apertures through which flow air from the plenum into the interior of the transition near the turbine end (more specifically, at the aft support). [0019] Another previous approach, described in U.S. Pat. No. 5,737,915, issued Apr. 14, 1998 to Lin et al., depicts a curved diffuser in which a pair of baffles within the flow area of the curved diffuser divide the flow area into three discrete flow passages. This is stated to provide for " . . . uniform flow distribution along the impingement sleeve about the transition region and thus achieves desirable static pressure recovery." However, this baffled curved diffuser is stated to be used in a gas turbine that comprises an impingement sleeve surrounding a transition piece. Also, the stated objective is to more evenly distribute compressor discharge flow about the impingement sleeve. This does not present a solution such as the present invention that achieves greater efficiency of air flow and pressure to the combustion chamber intakes. [0020] Having generally described the invention and differences between the present solution and previous approaches, the following embodiments are described, and are depicted in the figures so as to provide examples that include the best mode and that more fully explain various aspects of the invention. The following discussion also provides additional disclosure that further differentiates the invention from previous approaches and demonstrates how the invention more effectively and efficiently solves the above-stated problems. Continue reading about Gas turbine engine curved diffuser with partial impingement cooling apparatus for transitions... 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